Molten oxides are widely used as refining slag and mold flux in the steelmaking process. In the stationary state, the molten oxide and the molten iron form a layer due to their density difference. However, in the actual operation, they are partially mixed and dispersed as droplets, which can increase the slag-metal reaction area or cause the formation of nonmetallic inclusions. In this study, the dispersion behavior in density stratified flow was investigated by water model experiments. It was suggested that the dispersion behavior of silicone oil was affected by viscosity. As the kinematic viscosity was higher than 100 mm²/s, droplet generation tended to be less likely to occur.

The conventional equations for interface instability and energy balance underestimated the critical velocity of droplet generation when the kinematic viscosity of oil was higher than 100 mm²/s. On the other hand, we were able to reproduce the influence of viscosity in this experiment by applying the empirical formula using the Ohnesorge number. Furthermore, an energy balance formula including the influence of viscosity was newly constructed. We confirmed that the new formula agreed with the experimental results.

Used plastic waste flowing into ocean has become a worldwide problem. In recent years international trade in used waste plastics has been regulated. Therefore, a large amount of used plastic should be disposed domestically. On the other hand, used waste plastics with high calorific value could be used as an energy source. Then a gasification process of used plastics using fluidized bed has been newly developed. In this process, used plastics were decomposed in a fluidized bed reactor at around 600°C which was lower temperature than that used in current commercial processes. Higher calorific value gas could be attained by a gasification reaction control at the lower temperature. Hydrogen enriched gas generated from the water gas shift reaction of the basic oxygen furnace gas was used as fluidizing, or gasifying agent since hydrogen was considered to have an effect for promoting the decomposition reaction of hydrocarbon in used plastics. As fluid medium in the reactor, catalysts were used to improve gasification efficiency. In this study, the effect of gasification temperature and the type of the catalyst on a calorific value of produced gas and a gasification efficiency were investigated. High calorific value gas (LHV: 5000 kcal/Nm³) could be successfully produced from pyrolysis of used plastics by appropriate gasification temperature and catalyst.

In this study, we performed scanning transmission X-ray microscopy with a spatial resolution of approximately 50 nm to investigate the two-dimensional mapping of the chemical states of carbon in Fe–C alloy. The lamellar texture (pearlite) consisting of ferrite (α-Fe) and θ-Fe₃C with an interval of approximately 100 nm was identified by absorption from the carbon 1s→2p excitation in the X-ray absorption image. It was clearly observed that there exist more than two types of chemical states of carbon in θ-Fe₃C depending on the microtextures. The differences in chemical states were found between grained θ-Fe₃C and lamellar θ-Fe₃C in pearlite, which might have originated from the texture and morphology of the θ-Fe₃C. To consider the origins of the differences, we performed first-principles calculations by assuming the distortion and crystal anisotropy of the unit cell of the θ-Fe₃C structure. The results suggest that the anisotropy of the crystal structure of θ-Fe₃C and the lattice strain within lamellar θ-Fe₃C fail to explain the differences, and therefore, other factors should be considered.

In hot rolling process of low carbon steel sheets, oxide scale formed on the sheets may result in surface defects on the rolled products. The major phase of the scale is wustite FeO, which shows sufficient plasticity to follow the sheet deformation only at elevated temperature. However, thick scale is cracked, fragmented and indented to the sheets by the rolling even at elevated temperature because scale surface is instantly cooled by cold rolls to brittle temperature. Therefore, thick scale should be removed by descalers just before the rolling. It is reported that manganese decreases the eutectoid temperature between ductile wustite and brittle magnetite. Therefore, manganese may have a positive effect to widen wustite window to lower temperature and to suppress surface defects. In this study, 0 mass% and 2 mass% manganese bearing steel sheets with controlled scale on surface were hot rolled in a laboratory. The sheets were reduced 30% in thickness by unlubricated rolling at temperature between 1173 K and 1373 K. Scanning electron microscopy on longitudinal section showed that manganese decreases crack depth and increases spacing between scales indented to the steel. It is concluded manganese makes the scale on steel more ductile and suppresses surface defects.

In the gas wiping process for hot-dip galvanizing, the coating thickness has two thinning limits. The first is the limit due to splashing of the molten zinc liquid film, and the second is the thinning limit of the wiping capacity of the equipment.

In this study, we investigated the possibility that wiping efficiency is reduced by the effect of zinc solidification due to gas jet cooling by conducting a gas wiping experiment under various temperature conditions.

A galvanized steel strip with a width of 100 mm was immersed in a molten zinc bath in the air atmosphere. The steel strip was heated by induction heating or a gas burner, and the wiping gas was also heated.

The results clarified the fact that high temperature conditions improved gas wiping efficiency. It is suggested that high wiping efficiency is prevented by an increase in viscosity due to an increasing solid volume fraction in the liquid zinc film surface caused by microscopic solidification. In addition, it was also found that the development of the initial alloy layer reduced the liquid phase and prevented wiping.

To investigate the factor that cause the variation in friction coefficient by sliding conditions in commercially pure titanium coated titanium oxide film, in-situ observation of sliding interface during ball on block test and EBSD analysis of a sliding cross-section were performed. At the vertical load of 0.1 N, the friction coefficient stabilized at a low level of approximately 0.12. However, at 0.5 N, the friction coefficient varying widely in the range of 0.20–0.80. At 2.0 and 4.0 N, the friction coefficient stabilized at a high level, approximately 0.30 and 0.40, respectively. At the vertical load of 0.5 N, the friction coefficient was negatively correlated to the Taylor factor for the uniaxial compression of the titanium grains directly beneath the film . Thus, it can be presumed that the ploughing term of friction coefficient increased due to the enhancement of compressive strain of titanium. On the other hands, at vertical loads of 2.0 and 4.0 N, the ball is always in contact with multiple grains due to the larger contact area. As a result, it is considered that the influence of Taylor factor was equalized and the variation of friction coefficient got smaller.

We analyzed the crystal orientation of pure iron with two-way cold-rolling and subsequent annealing. As-received pure iron sheets were cold-rolled in the vertical direction against the cold-rolling direction of the as-received sheet, and then in the cold-rolling direction of the as-received sheet. The cold-rolled specimens were annealed in two conditions (short-term and long-term annealing). As short-term annealing, cold-rolled specimen was heated to desired temperature, and then water-quenched to room temperature (298 ± 2 K). As long-term annealing, cold-rolled specimen was heated to 1123 K and held for up to 180 min, and then furnace-cooled for up to 150 min and water-quenched to room temperature. The strain distribution of cold-rolled specimen was uniform, and Goss orientation grains were observed at the interface of α-fiber and γ-fiber and within the micro-shear bands in γ-fiber. By short-term annealing, Goss orientation grains within micro-shear bands grew, whereas those at the interface of α-fiber and γ-fiber disappeared. Abnormal grain growth of Goss orientation grains was attributed to the existence of grains having Σ9 grain boundaries against Goss orientation grains. In addition, existence of multiple adjacent Goss orientation grains played crucial role on the abnormal grain growth of Goss orientation grains.